Carnival's interiors are "eclectic." I have to admit I have never seen anyone say they thikn Carnival has the most beautiful ships in the world.
Personally, my theory is that the decor is intentionally inane just to make you forget your everyday standards of normality, lowering your inhibitions and making you giddy - and more likely to enjoy your cruise...
It's an odd strategy, but but seems to work. What do you think of when you see these interiors? (from Splendor)